Use concrete constrained extensions to get rid of protocol conformance trick.
Use concrete constrained extensions to get rid of protocol conformance trick.

Now that [SR-1009](https://bugs.swift.org/browse/SR-1009) is resolved, we can remove the FIXME and the extension can constrain to  the concrete `Version` type without needing any protocols
apple/swift-package-manager,JGiola/swift-package-manager,abertelrud/swift-package-manager,apple/swift-package-manager,vmanot/swift-package-manager,sschiau/swift-package-manager,abertelrud/swift-package-manager,apple/swift-package-manager,sschiau/swift-package-manager,vmanot/swift-package-manager,apple/swift-package-manager,abertelrud/swift-package-manager,JGiola/swift-package-manager,JGiola/swift-package-manager,sschiau/swift-package-manager,apple/swift-package-manager,abertelrud/swift-package-manager,JGiola/swift-package-manager,vmanot/swift-package-manager,sschiau/swift-package-manager,vmanot/swift-package-manager,JGiola/swift-package-manager,vmanot/swift-package-manager,abertelrud/swift-package-manager,sschiau/swift-package-manager